Organic electroluminescence is the phenomenon which excitons are formed in an (low molecular or high molecular) organic material thin film by re-combining holes injected through an anode with electrons injected through a cathode, and light with specific wavelength is generated by energy from the formed excitons.
Organic electroluminescent device using the above phenomenon has a basic structure as illustrated in FIG. 1.
The basic structure of the organic electroluminescent device includes a glass substrate 1, an indium-tin-oxide layer 2 (hereinafter, referred as “ITO layer”) formed on the upper side of the glass substrate 1 and acting as anode electrode, an insulating layer, an organic material layer 3, and a metal layer 4 acting as cathode electrode in the order. Walls W are formed to deposit the metal layers 4 separately on the ITO layer 2.
FIG. 2 is a plane view of the organic electroluminescent device shown in FIG. 1. For convenience, FIG. 2 shows a state that a cap 6 in FIG. 1 is removed from the device. As shown in FIG. 2, a plurality of ITO layers 2 and a plurality of metal layers 4 formed in an active area A are extended to the outer portion of the active area A, and each end portion of the layers 2 and 4 are concentrated on a part of the substrate 1 to form a pad P.
After the active area A consisted of the elements 2, 3, 4 and W is formed on the substrate 1 through the process as described above, the cap 6 is bonded to the substrate 1 by means of a sealant 5. The region to which the cap 6 is bonded is the outer portion of the substrate, that is, the outer region S1 and S2 of the active area A of the substrate 1. The entire active area A is isolated completely from the exterior by the cap 6, and only the pad P on which the ITO layers 2 (data lines) and the metal layers 4 (scan lines) extended to the outer portion of the active area A are concentrated is exposed to the exterior.
As shown in FIG. 1, a closed space is formed between the cap 6 and the substrate 1. The elements 2, 3, 4 and W placed in this space are not influenced by outer environment such as moisture and the like. On the other hand, the cap 6 is made from metal or glass, ultraviolet rays-curable adhesive is used as sealant 5. Also, a getter 8, which is moisture absorbent, is attached to a lower surface of a central portion of the cap 6 by a tape 7 made from organic material.
A process for bonding the metal cap 6 to the substrate 1 as described above is briefly described below with reference to FIG. 1, FIG. 2 and FIG. 3.
After the getter is attached to each of the metal caps 6 loaded in a cap tray (not shown), the sealant is dispensed on a substrate bonding-region (circumference surface) of the cap 6. After the cap 6 and the substrate 1 are aligned, the cap 6 is bonded to the region S1 and S2 formed at the outside of the active area A formed on the substrate 1. In order to bond the cap 6 securely to the substrate, ultraviolet rays are irradiated selectively on the cap-bonding region S1 and S2 of the substrate 1 to cure the sealant S. At this time, since the cap 6 is made from metal material which ultraviolet rays cannot penetrate, ultraviolet rays are irradiated to the glass substrate 1.
On the other hand, if ultraviolet rays are irradiated to the active area A, a threshold voltage of a drive transistor in the active matrix device is changed, and organic material in the passive matrix device is damaged to cause serious effect to the luminous function of the device.
In order to solve these problems, it is desirable that ultraviolet rays are not irradiated to the active area A of the substrate. Thus, a mask for curing the sealant is used to irradiate ultraviolet rays selectively to the substrate (portion corresponding to the sealant).
FIG. 3 is a view showing a relation between the mask used in the process for curing the sealant and the organic electroluminescent device. For convenience, only two organic electroluminescent devices (hereinafter, refer to as “device”) are shown in FIG. 3 and the other elements except the active area A are not shown therein.
The mask m used for curing the sealant is made from quartz having lower refractive index than glass, and a plurality of light non-transmittable layers m1 consisted of molybdenum (Mo) thin film or chrome (Cr) thin film are formed on corresponding areas to the active areas A formed on the substrate 10. On the other hand, in a process for bonding the caps loaded on a cap tray (not shown) to the substrate, a certain pressure is applied to the substrate 1, and this pressure is transmitted to the mask m which is contacted with the substrate 1. Therefore, in order to prevent transformation by such pressure, the mask m should have certain thickness.
Ultraviolet rays generated at an ultraviolet lamp (not shown) situated above the mask m penetrates the mask m, and then are irradiated onto the substrate 1. The ultraviolet rays penetrate the glass substrate 1 to cure the sealant. In the above process, on the other hand, the ultraviolet rays reach, but cannot penetrate the light non-transmittable layers m1. Therefore, the ultraviolet rays cannot reach the active areas A of the substrate 1 corresponding to the light non-transmittable layers m1.
Assuming that the ultraviolet rays penetrating the mask m are irradiated perpendicularly onto the substrate 1, the ultraviolet rays to be irradiated to each active area A can be completely intercepted by using the mask m on which the light non-transmittable layers m1 are formed. However, as shown in FIG. 4, it would be ideal for the ultraviolet rays penetrating the mask m to be irradiated perpendicularly onto the substrate 1 (a in FIG. 4), but such ideal radiation of ultraviolet rays is difficult to expect due to the structure of the ultraviolet generating device.
That is, in the ultraviolet generating device, the ultraviolet rays emitted from a light source are reflected on a glass plate which is one of the members constituting the ultraviolet generating device, and then irradiated to the mask m. Accordingly, the ultraviolet rays which are diffusively reflected on the glass plate are irradiated to the mask m with various angles of reflection.
Once the diffused ultraviolet rays are irradiated to the mask m which is made from quartz and has a certain thickness with a certain incident angle, the ultraviolet rays are refracted at the surface of the mask m, and then irradiated to the active area A of the substrate 1 (b in FIG. 4). Also, although the ultraviolet rays are irradiated in a direction perpendicular to the mask m, the ultraviolet rays can be refracted at the surface of the mask m, and then irradiated to the active area A of the substrate 1 (c in FIG. 4).
For the above reasons, the ultraviolet rays irradiated to the active area A have serious effect to the device's function. Therefore, the mask is needed to prevent the ultraviolet rays from being irradiated to the active area A in the process for curing the sealant.
On the other hand, the metal lines extended from the ITO layers (2 in FIG. 1) and the metal layers (4 in FIG. 1) in the active area A are formed on the region S1 and S2 to which the cap 6 is bonded, and so some of the ultraviolet rays penetrating the mask m are intercepted by the metal lines so that the ultraviolet cannot be irradiated to the sealant S.
Also, in this region S1 and S2 (in FIG. 2), the sealant 6 dispensed on the metal lines is not cured completely. Consequently, in order to cure the sealant completely, it is desirable to minimize the width of the metal lines in the regions S1 and S2 (in FIG. 2) to which the cap 6 is bonded.
Also, in case that the ultraviolet rays are irradiated to the substrate 1 by using the mask m, the precise alignment is needed between the mask m and the substrate 1 (that is, cap 6).